MD_DataIdentification

This is a bare-earth data lidar data set that was collected on November 27, 29 and
December 1, 2009 along the shoreline of the Cape Hatteras National Seashore in Dare
and Hyde Counties in North Carolina, after Nor'easter Ida. Binary point-cloud data
were produced from remotely sensed, geographically referenced elevation measurements
cooperatively by the U.S. Geological Survey (USGS) and the National Park Service (NPS).
Elevation measurements were collected over the area using the Experimental Advanced
Airborne Research Lidar (EAARL), a pulsed laser ranging system mounted onboard an
aircraft to measure ground elevation, vegetation canopy, and coastal topography. The
system uses high-frequency laser beams directed at the Earth's surface through an
opening in the bottom of the aircraft's fuselage. The laser system records the time
difference between emission of the laser beam and the reception of the reflected laser
signal in the aircraft. The plane travels over the target area at approximately 50
meters per second at an elevation of approximately 300 meters, resulting in a laser
swath of approximately 240 meters with an average point spacing of 2-3 meters. The
EAARL, developed originally by NASA at Wallops Flight Facility in Virginia, measures
ground elevation with a vertical resolution of 15 centimeters. A sampling rate of
3 kilohertz or higher, results in an extremely dense spatial elevation dataset. Over
100 kilometers of coastline can be easily surveyed within a 3- to 4-hour mission.
When subsequent elevation maps for an area are analyzed, they provide a useful tool
to make management decisions regarding land development.

These data depict the elevations at the time of the survey and are only accurate for
that time. Users should be aware that temporal changes may have occurred
since this data set was collected and some parts of this data may no longer represent
actual surface conditions. Users should not use this data for critical
applications without a full awareness of its limitations. Any conclusions drawn
from analysis of this information are not the responsibility of NOAA or any of its
partners. These data are NOT to be used for navigational purposes.

The data were collected using a Pilatus PC-6 aircraft. The Experimental Advanced Airborne
Research Lidar (EAARL) laser scanner collects the data using a green-wavelength (532-nanometer)
raster scanning laser, while a digital camera acquires a visual record of the flight.
The data are stored on hard drives and archived at the U.S. Geological Survey office
in St. Petersburg, Florida. The navigational data are processed and then, along with
the raw data, are downloaded into ALPS, or the Airborne Lidar Processing System (20091231
- 20101019). Data are converted from units of time to x,y,z points for elevation and
formatted into .las and .xyz files. The derived surface data can then also be converted
into raster data (GeoTIFFs). This process took place 20091127 through 20101102.

1

2010-12-23T00:00:00

Metadata imported into ArcCatalog from XML file.

1

2011-09-01T00:00:00

The NOAA Coastal Services Center (CSC) received files in unclassified LAS format.
The files contained LiDAR intensity and elevation measurements. CSC performed the
following processing on the data to make it available within Digital Coast: 1. The
unclassified data were processed to provide a bare earth surface. 2. The data were
converted from UTM, Zone 18 coordinates to geographic coordinates. 3. The data were
converted from NAVD88 heights to ellipsoid heights using Geoid09. 4. The LAS header
fields were sorted by latitude and updated.

1

2011-09-22T00:00:00

The NOAA National Geophysical Data Center (NGDC) received lidar data files via ftp
transfer from the NOAA Coastal Services Center. The data are
currently being served via NOAA CSC Digital Coast at http://www.csc.noaa.gov/digitalcoast/.
The data can be used to re-populate the system. The data are archived in LAS
or LAZ format. The LAS format is an industry standard for LiDAR data developed by
the American Society of Photogrammetry and Remote Sensing (ASPRS); LAZ is a loseless
compressed version of LAS developed by Martin Isenburg (http://www.laszip.org/). The
data are exclusively in geographic coordinates (either NAD83 or ITRF94). The data
are referenced vertically to the ellipsoid (either GRS80 or ITRF94), allowing for
the ability to apply the most up to date geoid model when transforming to orthometric
heights.